In one class of electronically controlled fuel injectors, a cam is utilized to drive a plunger within the injector body, and an electronically controlled spill valve is utilized to control timing of the injection event. Each injection event is initiated by closing the spill valve so that fuel pressure can build above a valve opening pressure that lifts the needle check valve and opens the nozzle outlet of the fuel injector. In many of these type of fuel injectors, the spill valve includes a solenoid attached to a spill valve member. Typically, low pressure fuel is allowed to circulate around the armature of the solenoid in order to avoid the need for internal sealing, which can be difficult to impossible to reliably accomplish.
While this spill valve technology has worked well in relatively small diesel engines that utilize distillate diesel fuel, relatively large diesel engines have been unable to adopt this technology since they burn heavy diesel fuel. Heavy diesel fuel has viscosity somewhere on the order of road tar at regular temperatures and must normally be heated to a temperature sometimes in excess of 400.degree. Fahrenheit in order to make the same sufficiently flowable through a fuel injection pump. Because of the extremely high viscosity of heavy diesel fuel, the current state of the art in relatively large diesel engines continues to be cam actuated fuel injection pumps that have no electronic timing control. The reason that the known spill technology cannot be incorporated into heavy diesel fuel injection systems is because the spill valve simply cannot be made to reliably perform when surrounded by relatively high viscosity heavy diesel fuel. Therefore, some other means must be devised for overcoming the problems of incorporating electronic control into heavy diesel fuel injection systems for relatively large diesel engines.
The present invention is directed to overcoming these and other problems, as well as generally improving electronically controlled fuel injection systems.